This application is based on Japanese Patent Application No. 2001-123081 filed on Apr. 20, 2001 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an engine control system with a cam sensor.
2. Description of the Related Art
The power for moving a car is generated by an internal combustion engine, which is also referred to hereafter simply as an engine. The engine is controlled by an engine control system. For example, the engine control system controls the engine""s injection of fuel and ignition timings in accordance with operating conditions of the car or operating conditions of the engine. The engine is controlled by injecting fuel into each cylinder or by carrying out an ignition for a certain stroke with a predetermined timing. It is thus necessary to identify the rotational position of the engine, that is, the rotational position or the rotational angle of the crankshaft, in order to execute the control of the engine. Processing to identify the rotational position of the engine is referred to as cylinder identifying processing in the case of a multi-cylinder engine. In the case of a multi-cylinder 4-stroke engine, for example, a reference position signal is used. This signal is detected only once in a rotation of the crankshaft. For instance, a crank sensor is provided in such a way that the reference position signal is generated when a specific one of the cylinders is positioned at the beginning of an air intake process. From the signal generated by the crank sensor, the engine control system identifies a cylinder that has arrived at a fuel-injection timing. Furthermore, the engine control system adjusts the fuel-injection timing to an optimum position. The engine control system can have a configuration typically based on a microcomputer and implementation of a fuel-injection timing and an ignition timing is controlled by using a timer.
A crank sensor comprises typically 34 teeth separated from each other by an angle of 10 degrees, leaving 2 consecutive locations each having no tooth as a reference position. In this configuration, the reference position may not be detected till a time corresponding to a maximum of 360 degrees CA (Crank Angle) lapses since a start of the engine. Thus, actions such as injection of fuel cannot be carried out till a time corresponding to the 360 degrees CA lapses since the activation of a starting motor by the driver. As a result, it may take a long time to start the engine.
In order to solve the above problem, there is provided a known conventional technology whereby fuel is injected asynchronously with the revolution of the engine till a reference position is detected. With such asynchronous injection of fuel, however, fuel cannot be injected with a proper timing. In addition, fuel cannot be injected into each cylinder at a proper volume. Thus, it is difficult to shorten the start period of the engine. In addition, it is feared that the emission worsens due to the asynchronous injection of fuel.
It is thus an object of the present invention to provide an engine control system capable of identifying the rotational position of the engine at an early time.
It is another object of the present invention to provide an engine control system having an improved start characteristic.
It is a further object of the present invention to provide an engine control system having an improved start characteristic and improved emission.
It is a still further object of the present invention to improve the start characteristic of an engine having a variable valve timing unit.
In accordance with a first aspect of the present invention, an engine control system employed in a multi-cylinder engine is provided with a crank sensor and a cam sensor. The engine control system further has a second identifying means for identifying a rotational position of the engine on the basis of a signal output by the cam sensor and a first identifying means for identifying a rotational position of the engine on the basis of a signal output by the cam sensor and a signal output by the crank sensor. In this configuration, there is provided the second identifying means for identifying a rotational position of the engine by using the cam sensor besides to the first identifying means for identifying a rotational position of the engine by using the crank sensor. Thus, since either of the identifying means identifies a rotational position of the engine, the rotational position of the engine can be recognized at an early time. As a result, the engine can be controlled at the early time in accordance with the rotational position of the engine.
In accordance with a second aspect of the present invention, an engine control system is provided with a first cam sensor installed on a first camshaft and a second cam sensor set on a second camshaft. The engine control system further has a cylinder identifying means for identifying a rotational position of the engine on the basis of a signal output by the first cam sensor and a signal output by the second cam sensor. In this configuration, a rotational position of the engine can be identified by using only 2 cam sensors.
In accordance with a third aspect of the present invention, an engine control system is provided with a crank sensor for generating a signal indicating a first reference position and a cam sensor for generating a signal indicating a second reference position different from the first reference position. The signals generated by the crank and cam sensors are used for controlling a variable valve timing unit. The first reference position detected by the crank sensor is used by a first engine control means to control the engine. On the other hand, the second reference position detected by the cam sensor is used by a second engine control means to control the engine at least during a period of time ending with first detection of the first reference position. With this configuration, when the engine is started, either the first reference position or the second reference position is detected first. Thus, the engine can be controlled at an early time in accordance with the rotational position. In addition, the cam sensor can be utilized also for controlling the variable valve timing unit.